Electronic device having path of power supplied to display part switched according to whether external power is supplied

ABSTRACT

An electronic device operable from one of an external power supply and a battery. The electronic device includes a display part, a power converter, an inverter generating an operating voltage for the display part, a system part generating information to be displayed on the display part and operable from an output of the power converter, a battery, an input power detector, and a switching controller. The switching controller controls power to the inverter so that where the input power detector detects availability of an external power, the switching controller supplies the external power to the power converter and the power converter supplies power to the inverter to generate the operating voltage for the display part; and where the input power detector detects the external power is not available, the switching system supplies battery power to the power converter and the inverter independently.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Korean Patent Application No.2005-31626, filed Apr. 15, 2005, in the Korean Intellectual PropertyOffice, the disclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

An aspect of the present invention relates to an electronic device, andmore particularly, to an electronic device wherein a path of powersupplied to display is switched according to whether external power issupplied.

2. Description of the Related Art

Electronic devices employing batteries are widely used to enableportability and mobility. Such electronic devices include portablecomputers like laptop computers, notebook computers, personal digitalassistants (PDA); mobile phones; CD players; video camcorders; etc.Generally, the electronic devices are provided with a connectionterminal for connecting an adapter to use external power through anAC/DC adapter, as well as a battery. A secondary battery which isrechargeable is employed in the electronic devices and is recharged bypower from the adapter.

The electronic devices may be provided with a display panel to displayan image thereon, and a liquid crystal display (LCD) panel is widelyused as the display panel.

The LCD panel is a light-receiving display panel unlike a cathode raytube (CRT) or a plasma display panel (PDP), and includes a lamp toprovide light.

FIG. 1 illustrates an example of a power supply system of a conventionalportable computer. As shown in FIG. 1, the portable computer includes anadapter 110 and a battery 111 to supply power; a battery charger 112 tocharge the battery 111 by using power from the adapter 110; an adapterdetector 113 to detect whether the adapter 110 is connected; an LCDpanel 116; a lamp 115 to emit light to the LCD panel 116; an inverter114 to receive power from the adapter 110 or the battery 111 and convertthe power into alternating current power for driving the lamp 115; and asystem power supply 120a to convert the power from the adapter 110 orthe battery 111 into power for driving a system part 117.

The power from the adapter 110 or the battery 111 is supplied to thesystem power supply 120 a and the inverter 114 according to switchingmovement of a VDC switch 118 in response to the detection of the adapterdetector 113. The adapter detector 113 and the VDC switch 118 controlthe power supplied from the adapter 110 to be supplied to the systempower supply 120 a and/or the inverter 114, prior to the power suppliedfrom the battery 111.

The system power supply 120 a converts the power supplied from theadapter 110 or the battery 111 into power for driving the system part117 to supply the converted power to each of electronic components ofthe system part 117. The system power supply 120 a includes DC/DCconverters 121 a and 122 a, e.g., a switching voltage regulator, tooutput power at different voltage levels. An inverter switch 137 isprovided to cut off power supplied to the inverter 114.

In the power supply system shown in FIG. 1, a voltage level of the powerinput to the inverter 114 ranges from a voltage level of power outputfrom the adapter 110 to a voltage level output by the battery 111. Forexample, if the voltage level of output power of the battery 111 is 9Vto 11.1 V (for a 3S battery) and the voltage level of the output powerof the adapter 110 is 19V, the voltage level of the input power of theinverter 114 ranges from 9V to 19V.

The inverter 114 is designed to have a breakdown voltage correspondingto 19V to satisfy the input voltage of 9V to 19V and duty fluctuationbecomes large, thereby preventing a realization of high efficiency inselecting a MOSFET as a switching element and in designing a highvoltage transformer.

FIG. 2 illustrates another example of a power supply system of anotherconventional portable computer. Unlike the power supply system of theportable computer shown in FIG. 1, the power supply of the portablecomputer shown in FIG. 2 supplies the inverter 114 with power from oneof DC/DC converters 121 b and 122 b of a system power supply 120 b,thereby maintaining a voltage level of power input to the inverter 114,for example, at 5V.

However, while the battery 111 supplies power, in the power supplysystem of the portable computer shown in FIG. 2, the power from thebattery 111 is input to the inverter 114 through the DC/DC converter 122b of the system power supply 120 b and goes through a power conversionprocess twice, thereby lowering conversion efficiency of the DC/DCconverter 122 b and the inverter 114 corresponding to load in view ofthe battery 111, and thus losing electric power unnecessarily. That is,the conversion efficiency of the DC/DC converter 122 b and the inverter114 should be more than 95%, respectively, to maintain the conversionefficiency of the load of more than 90% with respect to the input to thebattery 111. However, it is difficult to realize the DC/DC converter 122b and the inverter 114 with more than the 95% conversion efficiency.

SUMMARY OF THE INVENTION

Accordingly, an aspect of the present invention is to provide anelectronic device which selectively supplies power output from a systempower converter and a battery to a display power converter to realize anarrow input voltage range of input power to the display power converterdepending on whether external power is supplied, and increases a usagetime of the battery by improving design efficiency of the display powerconverter.

The foregoing and/or other aspects of the present invention are achievedby providing an electronic device which receives power from one of anexternal power supply and a battery outputting first power to drive theelectronic device. The electronic device includes a display part; asystem power converter to convert the external power supplied from theexternal power supply into second power at a preset voltage level; adisplay power converter to convert one of the first power and the secondpower into power for driving the display part and supply it to thedisplay part; and a power controller to supply the second power from thesystem power converter as input power of the display power converter ifdetected that the external power is supplied from the external powersupply, and supply the first power from the battery as the input powerof the display power converter if the external power is cut off from theexternal power supply.

According to an aspect of the present invention, the electronic devicemay include a system part to display an image through the display part,wherein the system power converter receives the first power if theexternal power is cut off from the external power supply to convert itinto the second power, and the second power output from the system powerconverter is supplied as power for driving the system part.

According to an aspect of the present invention, the display part mayinclude a light-receiving display panel to display an image thereon anda lamp to emit light to the display panel to display the image on thedisplay panel, wherein the display power converter comprises an inverterto convert the first power or the second power into alternating currentpower for driving the lamp, and supply the alternating current power tothe lamp.

According to an aspect of the present invention, the display panel mayinclude a liquid crystal display (LCD) panel.

According to an aspect of the present invention, the power controllermay include a power switch which is switched to supply one of the firstpower and the second power to the inverter; and a switching controllerto control the switch corresponding to the supply of the external power.

According to an aspect of the present invention, the power switch mayinclude a first switch to control the first power to be supplied to theinverter and a second switch to control the second power to be suppliedto the inverter.

According to an aspect of the present invention, the second switch mayinclude a switching element to control the second power to be suppliedto the inverter and a diode which is connected in parallel with theswitching element to cut off power from the inverter to the system powerconverter.

According to an aspect of the present invention, the second power isincluded in the range of the voltage level of the first power.

According to an aspect of the present invention, the first power fromthe battery which is supplied as the input power of the display powerconverter does not pass through the system power converter in the statewhere the supply of the external power is cut off from the externalpower supply.

The foregoing and/or other aspects of the present invention are achievedby providing an electronic device which receives power from one of anexternal power supply and a battery outputting first power. Theelectronic device includes a display part; a system part to display animage through the display part; a plurality of system power convertersto convert one of the external power supplied from the external powersupply and the first power into a second power at different voltagelevels for driving the system part; a display power converter to convertone of the second power output from one of the plurality of system powerconverters and the first power into a power for driving the displaypart, and supply the converted power to the display part; and a powercontroller to supply the second power from one of the plurality ofsystem power converters as an input power of the display power converterif detected that the external power is supplied from the external powersupply, and supply the first power from the battery as the input powerof the display power converter if the external power is cut off from theexternal power supply.

According to an aspect of the present invention, a voltage level of thesecond power supplied to the display power converter is close to avoltage level of the first power.

According to an aspect of the present invention, the power controllermay include a power switch which is switched to supply one of the firstpower and the second power to the inverter; and a switching controllerto control the switch corresponding to the supply of the external power.

Additional aspects and/or advantages of the invention will be set forthin part in the description which follows and, in part, will be obviousfrom the description, or may be learned by practice of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages of the invention will becomeapparent and more readily appreciated from the following description ofthe embodiments, taken in conjunction with the accompanying drawings ofwhich:

FIGS. 1 and 2 illustrate a power supply system of a conventionalelectronic device;

FIG. 3 is a control block diagram of an electronic device according to afirst embodiment of the present invention;

FIG. 4 is a control block diagram of an electronic device according to asecond embodiment of the present invention; and

FIG. 5 illustrates the relation between a voltage level of input powerof an inverter and efficiency of the inverter.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Reference will now be made in detail to the present embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings, wherein like reference numerals refer to the like elementsthroughout. The embodiments are described below in order to explain thepresent invention by referring to the figures.

An electronic device according to a first embodiment of the presentinvention receives power from one of an external power supply and abattery to drive the electronic device. That is, the electronic devicemay receive power from the external power supply or the battery. Asshown in FIG. 3, the electronic device according to the first embodimentincludes display parts 15 (lamp) and 16 (LCD panel), a battery 11, asystem power supply 20 a, and a power controller 30. The electronicdevice may also include an external power supply (hereinafter, to bereferred to as an adapter) such as an adapter 10, etc., to supplyexternal power.

A system part 17 includes a plurality of electronic components toperform major functions of the electronic device. For example, if theelectronic device according to an embodiment of the present invention isprovided as a portable computer, the system part 17 may include a CPU, amemory such as a RAM, etc., a chipset, a main board and a graphic card.Here, the system part 17 receives power from the system power supply 20a.

The battery may be provided as a secondary battery 11 which isrechargeable by a battery charger 12. For example, a lithium-ion batteryor other rechargeable secondary battery may be used.

Here, the battery 11 includes at least one battery cell with aspecification about a voltage level of a first power as a recharging andoutput power thereof. As an example of the first embodiment according tothe present invention, the battery 11 may include three battery cells.

A maximum voltage level of power output from the respective batterycells is 3.7V, and a cut-off voltage of the respective battery cells is3V as an example. Accordingly, the voltage level of the first poweroutput from the battery 11 having the three battery cells is 9V to11.1V.

The adapter 10 may include an AC/DC adapter to convert commercialalternating current power used at home, etc., into direct current power.Alternatively, the adapter 10 may be a DC/DC adapter to use directcurrent power such as a cigar jack for vehicles as input power. Theelectronic device according to the first embodiment of the presentinvention receives the external power from the adapter 10, and a voltagelevel of the external power supplied from the adapter 10 is 19V as anexample.

The system power supply 20 a converts the external power supplied fromthe adapter 10 when the adapter 10 is connected or converts a firstpower supplied from the battery 11 into power at various voltage levelsfor driving the system part 17, and supplies the converted power to thesystem part 17. For example, if the electronic device is provided as aportable computer, the system power supply 20 a outputs power at voltagelevels, e.g., 5V, 3.3V, 2.5V, etc., for driving the respectiveelectronic components of the system part 17. The power at variousvoltage levels which is output from the system power supply 20 a is usedfor driving the respective electronic components and transmitting asignal, as necessary.

The system power supply 20 a may include a plurality of system powerconverters, e.g., DC/DC converters 21 a and 221 a, each including, forexample a switching voltage regulator to generate power at a specifiedvoltage level. Hereinafter, the system power converters will bedescribed as the DC/DC converters 21 a and 221 a as an example.

The display parts 15 and 16 may include a light-receiving display panelto display an image thereon; and a lamp 15 to emit light to the displaypanel 16 to display the image on the display panel 16. Thelight-receiving display panel will be described as an LCD panel 16 as anexample, as shown in FIG. 3. Further, the LCD panel 16 may comprise alight-receiving display panel which displays the image by receivinglight from the lamp 15.

The display power converter supplies power to the display part 15 and16. Here, the display power converter includes an inverter 14 to supplyalternating current power for driving the lamp 15, as an example.

The inverter 14 receives either the first power from the battery 11 orsecond power supplied from one (hereinafter, referred to as an inverterDC/DC converter 221 a) of the plurality of DC/DC converters 21 a and 221a of the system power supply 20 a to convert the received power intopower for driving the lamp 15, and supplies the converted power to thelamp 15.

The inverter DC/DC converter 221 a converts the external power from theadapter 10 or the first power from the battery 11 into the second powerat a preset voltage level to supply the converted power to the inverter14.

If the external power is supplied, the power controller 30 controls thesecond power output from the inverter DC/DC converter 221 a to besupplied to the inverter 14. If the power from the adapter 10 is cutoff, for example, if a user disconnects the adapter 10 or a usage powerconnected with the adapter 10, the power controller 30 controls thefirst power output from the battery 11 to be supplied to the inverter14. Accordingly, if the external power is input from the adapter 10, theexternal power is converted into the second power by the inverter DC/DCconverter 221 a to be supplied to the lamp 15 for driving the lamp 15.If the external power is not input, the first power output from thebattery 11 is directly applied to the inverter 14, thereby reducingpower loss by unnecessary conversion by the inverter DC/DC converter 221a and increasing usage time of the battery 11.

The electronic device shown in FIG. 3 may comprise an adapter detector13 to detect whether the external power is supplied from the adapter 10.The power controller 30 may determine the supply of the external powercorresponding to the detection of the adapter detector 13. The powercontroller 30 a may comprise a power switch 31 and a switchingcontroller 38.

The power switch 31 switches one of the first power output from thebattery 11 and the second power output from the inverter DC/DC converter221 a to the inverter 14, according to the control of the switchingcontroller 38.

The power switch 31 may include a first switch 34 to control the firstpower output from the battery 11 to be supplied to the inverter 14; anda second switch 37 to control the second power output from the inverterDC/DC converter 221 a to be supplied to the inverter 14. That is, theinverter 14 is supplied from the DC/DC converter 221 a or directly fromthe battery 11.

The first switch 34 may include a first switching element 32 which isswitched according to the control of the switching controller 38 tocontrol the connection between the battery 11 and the inverter 14; and afirst diode 33 which is connected in parallel with the first switchingelement 32. Here, a cathode of the first diode 33 is connected to thebattery 11 and an anode of the first diode 33 is connected to theinverter 14. Accordingly, if the voltage level of the first power outputfrom the battery 11 is larger than a voltage level of the second poweroutput from the inverter DC/DC converter 221 a, the first power from thebattery 11 may be prevented from being supplied to the inverter 14 whenthe first switch 34 is turned off.

The second switch 37 may include a second switching element 35 which isswitched according to the control of the switching controller 38 tocontrol the connection between the inverter DC/DC converter 221 a andthe inverter 14; and a second diode 36 which is connected in parallelwith the second switching element 35. An anode of the second diode 36 isconnected to the inverter DC/DC converter 221 a and a cathode thereof isconnected to the inverter 14. Accordingly, when the first switchingelement 32 is turned on and the second switching element 35 is turnedoff by the control of the switching controller 38 to supply the firstpower from the battery 11 to the inverter 14, the first power at thelarger voltage level than the second power is prevented from flowing tothe inverter DC/DC converter 221 a.

The switching controller 38 turns on and off the first switching element32 and/or the second switching element 35 according to the detection ofthe adapter detector 13. That is, the switching controller 38 turns offthe first switching element 32 and turns on the second switching element35 if the adapter detector 13 detects that the external power issupplied from the adapter 10.

Meanwhile, the switching controller 38 turns off the second switchingelement 35 and turns on the first switching element 32 if the adapterdetector 13 detects that the external power is not supplied from theadapter 10.

The voltage level of the second power output from the inverter DC/DCconverter 221 a may be close to the voltage level of the first poweroutput from the battery 11. As described above, if the voltage levels ofthe power output from the respective DC/DC converters 21 a and 221 a ofthe system power supply 20 a are +5V, +3.3V and +2.5V and the voltagelevel of the first power output from the battery 11 is in the range of9V to 11.1V, the DC/DC converter 22 a outputting a power of 5V among theDC/DC converters 21 a and 221 a of the system power supply 20 a may beused as the inverter DC/DC converter 22 a. Also, if one of the DC/DCconverters 21 a and 22 a of the system power supply 20 a outputs powerat the voltage level included in the range of 9V to 11.1V which is thesame as the voltage level of the first power output from the battery 11,the corresponding DC/DC converters 21 a and 22 a may be used as theinverter DC/DC converter 22 a. Then, the voltage level of the inputpower to the inverter 14 (INV_VDC) becomes 9V to 11.1V, thereby reducinga design margin of the inverter 14. That is, a narrow INV_VCD may berealized with respect to an input of the inverter 14, so that theinverter 14 can use a low breakdown voltage by the realization of thenarrow INV_VDC, thereby reducing switching loss and conduction loss andultimately increasing usage time of the battery 11. Thus, the voltageoutput from the DC/DC converter 22 a may be within about 20% of thevoltage output by the battery 11.

FIG. 5 illustrates the relation between the voltage level of the inputpower of the inverter 14 and efficiency of the inverter 14. As shown inFIG. 5, the lower the voltage level of the input power and the narrowerthe fluctuation of the voltage level of the input power is, the higherthe efficiency of the inverter 14 is. Accordingly, if the narrow INV_VDCis realized with respect to the input of the inverter 14, the battery 11is used longer due to efficiency improvement of the inverter 14. Cases1-4, as shown, represent results of testing four samples subjected to asame testing condition.

In the embodiment shown in FIG. 3, a VDC switch 18 makes one of theexternal power from the adapter 10 and the first power from the battery11 to be supplied to the system power supply 20 a and/or the DC/DCconverters 21 a and 22 a. That is, the switch 18 supplies the externalpower from the adaptor 10 or the first power from the battery 11 to thesystem power supply 20 a and/or the DC/DC converters 21 a and 22 a. TheVDC switch 18 may switch according to the control of the switchingcontroller 38. The switching controller 38 controls the VDC switch 18 tosupply the external power from the adapter 10 to the system power supply20 a and/or the DC/DC converters 21 a and 22 a, prior to the power fromthe battery 11.

An electronic device according to a second embodiment of the presentinvention will be described with reference to FIG. 4.

The electronic device shown in FIG. 4 includes a display powerconverter, for example, a DC/DC converter 22 b, which converts externalpower from an adapter 10 into second power at a preset voltage level tosupply it to an inverter 14, and a system power supply 20 b. As shown inFIG. 4, the DC/DC converter 22 b receives first power outputted from abattery 11 when power from the adapter 10 is cut off. Even if a userdisconnects the adapter 10 while using the electronic device in thestate that the electronic device is connected with the adapter 10, theinverter 14 is continuously supplied with power by the first poweroutputted from the battery 11 until the power inputted to the inverter14 is converted from the second power to the first power according to aswitching movement of a power switch 31 of a power controller 30.

Like in the first embodiment shown in FIG. 3, the power controller 30controls the second power output from the DC/DC converter 22 b to besupplied to the inverter 14 if the supply of the external power isdetected. Conversely, if the supply of the external power is notdetected, the power controller 30 controls the first power output fromthe battery 11 to be supplied to the inverter 14.

A voltage level of the second power output from the DC/DC converter 22 baccording to the second embodiment of the present invention may be closeto a voltage level of the first power output from the battery 11. Thevoltage level of the second power output from the DC/DC converter 22 bmay be included in the range of the voltage level of the first poweroutput from the battery 11. As described above and as can be seen fromFIG. 5, if the voltage level of the first power output from the battery11 is in the range of 9V to 11.1V, the voltage level of the second poweroutput from the DC/DC converter 22 b may be included in the range of 9Vto 11.1V, for example, 10V. Then, the voltage level of the input powerto the inverter 14 becomes 9V to 11.1V, thereby reducing a design marginof the inverter 14. That is, a narrow INV_VDC may be realized withrespect to an input of the inverter 14, thereby reducing switching lossand ultimately increasing usage time of the battery 11 due to therealization of the narrow INV_VDC.

Where electronic components of the system part 17 include an electroniccomponent which uses a power corresponding to the voltage level of thesecond power, the second power output from the DC/DC converter 22 b mayalso supply power to the corresponding electronic component.

Although a few embodiments of the present invention have been shown anddescribed, it would be appreciated by those skilled in the art thatchanges may be made in this embodiment without departing from theprinciples and spirit of the invention, the scope of which is defined inthe claims and their equivalents.

1. An electronic device operative from one of an external power supplyand a battery outputting first power, the electronic device comprising:a display part; a system power converter to convert the external powersupplied from the external power supply into second power at a presetvoltage level; a display power converter to convert one of the firstpower and the second power into power for driving the display part andsupply the converted power to the display part; and a power controllerto supply the second power from the system power converter as inputpower of the display power converter if detected that the external poweris supplied from the external power supply, and supply the first powerfrom the battery as the input power of the display power converter ifthe external power is cut off from the external power supply.
 2. Theelectronic device according to claim 1, further comprising a system partto display an image through the display part, wherein the system powerconverter receives the first power if the external power is cut off fromthe external power supply to convert the first power into the secondpower, and the second power output from the system power converter issupplied as power for driving the system part.
 3. The electronic deviceaccording to claim 1, wherein the display part comprises alight-receiving display panel to display an image thereon and a lamp toemit light to the display panel to display the image on the displaypanel, wherein the display power converter comprises an inverter toconvert the first power or the second power into alternating currentpower for driving the lamp, and supply the alternating current power tothe lamp.
 4. The electronic device according to claim 3, wherein thedisplay panel comprises a liquid crystal display (LCD) panel.
 5. Theelectronic device according to claim 3, wherein the power controllercomprises: a power switch which is switched to supply one of the firstpower and the second power to the inverter; and a switching controllerto control the switch corresponding to the supply of the external power.6. The electronic device according to claim 5, wherein the power switchcomprises: a first switch to control the first power to be supplied tothe inverter; and a second switch to control the second power to besupplied to the inverter.
 7. The electronic device according to claim 6,wherein the second switch comprises a switching element to control thesecond power to be supplied to the inverter and a diode which isconnected in parallel with the switching element to cut off power fromthe inverter to the system power converter.
 8. The electronic deviceaccording to claim 1, wherein a voltage range of the second power isincluded in a range of the voltage level of the first power.
 9. Theelectronic device according to claim 1, wherein the first power from thebattery which is supplied as the input power of the display powerconverter does not pass through the system power converter in the statewhere the supply of the external power is cut off from the externalpower supply.
 10. An electronic device operative from one of an externalpower supply and a battery outputting first power, the electronic devicecomprising: a display part; a system part to display an image throughthe display part; a plurality of system power converters to convert oneof the external power supplied from the external power supply and thefirst power into a second power at different voltage levels for drivingthe system part; a display power converter to convert one of the secondpower output from one of the plurality of system power converters andthe first power into a power for driving the display part, and supplythe converted power to the display part; and a power controller tosupply the second power from one of the plurality of system powerconverters as an input power of the display power converter if detectedthat the external power is supplied from the external power supply, andsupply the first power from the battery as the input power of thedisplay power converter if the external power is cut off from theexternal power supply.
 11. The electronic device according to claim 10,wherein a voltage level of the second power supplied to the displaypower converter is close to a voltage level of the first power.
 12. Theelectronic device according to claim 10, wherein the display partcomprises a light-receiving display panel to display an image thereonand a lamp to emit light to the display panel to display the image onthe display panel, wherein the display power converter comprises aninverter to convert the first power or the second power into alternatingcurrent power for driving the lamp, and supply the alternating currentpower to the lamp.
 13. The electronic device according to claim 12,wherein the display panel comprises a liquid crystal display (LCD)panel.
 14. The electronic device according to claim 12, wherein thepower controller comprises a power switch which is switched to supplyone of the first power and the second power to the inverter; and aswitching controller to control the switch corresponding to the supplyof the external power.
 15. The electronic device according to claim 14,wherein the power switch comprises a first switch to control the firstpower to be supplied to the inverter and a second switch to control thesecond power to be supplied to the inverter.
 16. The electronic deviceaccording to claim 15, wherein the second switch comprises a switchingelement to control the second power to be supplied to the inverter and adiode which is connected in parallel with the switching element to cutoff power from the inverter to the system power converter.
 17. Theelectronic device according to claim 10, wherein the first power fromthe battery which is supplied as the input power of the display powerconverter does not pass through the system power converter in the statewhere the supply of the external power is cut off from the externalpower supply.
 18. The electronic device according to claim 11, wherein avoltage level of the second power supplied to the display powerconverter is within about 20 percent of a voltage level of the firstpower.
 19. An electronic device, comprising: a display part; a powerconverter; an inverter generating an operating voltage for the displaypart; a system part generating information to be displayed on thedisplay part and operable from an output of the power converter; abattery; an input power detector which detects an availability ofexternal power; and a switching controller controlling power to theinverter and the power converter, wherein: where, in a first mode, theinput power detector detects the availability of the external power, theswitching system supplies the external power to the power converter andto the inverter via the power converter; and where, in a second mode,the input power detector detects that the external power is notavailable, the switching system supplies battery power to the powerconverter and to the inverter independently of the power converter. 20.The electronic device of claim 19, wherein: where the switchingcontroller is supplying the external power to the power converter andthe input power detector detects a loss of the external power, theswitching controller supplies battery power to the power converter andto the inverter via the power converter during a time of transition fromthe first mode to the second mode.
 21. The electronic device of claim19, wherein: the power converter supplies power to a component of theelectronic device other than the inverter generating the operatingvoltage for the display part.
 22. The electronic device of claim 19,wherein: the power supplied to the inverter via the power converter andthe power supplied to the inverter from the battery independent of thepower converter have respective voltages which are equal within about 20percent.